Device and method for predistorting and input signal

ABSTRACT

A device, comprising a storage means ( 51 ) for storing phase change values, and a phase offset adding means ( 50 ) for predistorting an input signal at an amplifier means is disclosed. A controller means ( 52 ) is connected to the storage means ( 52 ) and the phase offset adding means ( 50 ). Said controller means ( 52 ) is adapted to retrieve phase change values from the storage means ( 51 ), and output an offset signal to the phase offset adding means ( 50 ), which is adapted to add said offset signal to the input signal. The invention also discloses a method for predistorting an input signal at an amplifier means ( 30 ) by retrieving phase change values from a look-up table stored in the storage means ( 30 ) in response to an indication to change the gain level of the amplifier means ( 30 ).

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/441,459 filed on Jan. 21, 2003,and claims priority from European Patent Application No. 03000495-6filed on Jan. 13, 2003. This application is a U.S. national stageapplication of International Application No. PCT/EP2003/011938.

TECHNICAL FIELD

The present invention relates to a device and a method for predistortingan input signal at an amplifier means of a transmitter chain. Inparticular, the invention relates to the compensation of phase jumps inthe output power of an output signal caused by the changing of the powerlevel of the output signal.

DESCRIPTION OF RELATED ART

In mobile communication several techniques for transmitting informationfrom a mobile terminal, such as a mobile telephone, a pager, acommunicator, i.e. an electronic organizer, a smartphone or the like, toa base station are available. The communication techniques include e.g.frequency division multiple access (FDMA), time division multiple access(TDMA), and code division multiple access (CDMA). One communicationtechnology being based on the CDMA technology is the wideband codedivision multiple access (WCDMA) currently being employed for theuniversal mobile telecommunication system (UMTS) being developed withinthe third generation partnership project (3GPP).

In CDMA systems the over-the-air power control of the channel betweenthe mobile terminal and the base station is a vital issue. An UMTS basestation averages many channel estimates from a signal sent in differentslots from a transmitter of a mobile terminal when it is possible, suchas when the mobile is not moving or is moving very slow. This will givea large improvement of performance since the pilot symbol comprised ineach slot of the signal from the mobile terminal is always very weak.One requirement for this to work is that the channel remainssubstantially constant despite that the mobile terminal changes itsoutput power. The environment of the mobile terminal, and the distancebetween the mobile terminal and the base station effects the power levelof the signal received by the base station. Also, the power received bythe base station is dependent on the wanted data rate in the up-link.Therefore, the output power from the transmitter of the mobile terminalis changed for meeting the requirement that the power of the up-linkchannel from the mobile terminal should remain substantially constantwhen received by a base station. To provide the changing of the outputpower of the transmitter of the mobile terminal, said transmittercomprises an amplifier having variable gain. The gain of the variablegain amplifier may be changed in levels, so as to adjust the power ofthe output signal from the transmitter of the mobile terminal accordingto certain predetermined levels.

It has turned out that changing the output power of the variable gainamplifier is difficult without affecting the phase of the transmittedsignal. Waveform generators known in the art generating the input signalto the variable gain amplifier can not compensate for phase jumps beingsynchronized with the output power change, which e.g. is described inthe 3GPP specification TS 25.101. The link performance, i.e. the linkbetween the mobile terminal and the base station, is degraded by thephase shift in the transmitter of the mobile terminal. Therefore, it ispreferred to keep the phase-shift of the output power as low as possiblewhen changing the power level.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a device for compensatingfor phase-shifts in the output power of an output signal from atransmitter chain of an electronic equipment, such as a mobile terminal,a mobile telephone, a pager, or a communicator, said phase-shiftsoccurring as time discrete phase-jumps in response to changing theoutput power of the output signal. Another object of the invention is toprovide a device capable of compensating for temperature dependentphase-shifts of the output power. Still another object of the inventionis to provide a device capable of compensating for frequency orfrequency band dependent phase-shifts of the output power. Also, it isan object of the invention that the compensation of the phase-shift willnot be detrimental to the output power.

A device comprising a storage means and a phase offset adding meansconnected to a controller means achieves the above objects. Thecontroller means is adapted to retrieve phase change values stored in alook-up table of the storage means. Based on first and second phasechange values corresponding to a current and a new gain level of anamplifier means, the controller means is adapted to calculate a phaseoffset value. A signal comprising the phase offset value is supplied tothe phase offset adding means, which is adapted to add the phase offsetvalue to an input signal at the amplifier means.

In one embodiment, the phase offset signal is a complex value having aphase value corresponding to the calculated phase offset value. Bysynchronizing the adding of the phase offset signal to the input signalwith the changing of the gain level of the amplifier means in a time gapbetween slots, wherein information data is transmitted, the adding ofthe phase offset signal will not be detrimental to the output power. Theinput signal is a base band signal generated by a waveform generator.The phase offset adding means of the device according to the inventionis in one embodiment provided after first and second transmit filters ofthe waveform generator.

In another embodiment, said phase offset adding means is provided priorto said filters of the waveform generator. Further, the controller meansis further adapted to receive an indication that the gain level of theamplifier means is to be changed, said indication comprising the currentand the new gain levels of the amplifier means. Each phase change valueof the storage means corresponds to the change of the phase of theoutput power of the amplifier means when the gain level of saidamplifier means is changed from a first reference level, such as thelowest gain level, to a second predetermined gain level. Changing thegain level of the amplifier means will change the output power to apredetermined level. In alternative embodiments of the device accordingto the invention, said device comprises a temperature sensing meansand/or a frequency indicator, wherein the device is adapted tocompensate for temperature and/or frequency dependent phase-shifts.

Another object of the invention is to provide a method for compensatingphase-shifts of an output signal from a transmitter chain of anelectronic equipment, said phase-shifts occurring as time discretephase-jumps in response to changing the output power of the outputsignal. Also, it is an object of the invention to provide a method forcompensating for temperature dependent phase-shifts of the outputsignal. Still another object is to provide a method for compensating forfrequency dependent phase-shifts of the output signal.

These objects are achieved by a method for predistorting an input signalat an amplifier means comprising the steps of: retrieving from a storagemeans phase change values; calculating a phase offset value based on theretrieved change values; and adding the phase offset value to the inputsignal. In an alternative embodiment a temperature or a temperatureinterval is derived, and temperature dependent phase change values areretrieved from the storage means, wherein a temperature dependent phaseoffset signal is added to the input signal. In still en alternativeembodiment a frequency or frequency interval is derived, and frequencydependent phase change values are retrieved from the storage means,wherein a frequency dependent phase offset signal is added to the inputsignal.

It is another object of the invention to provide an electronic equipmentcapable of compensating for phase-shifts of the output power of anoutput signal from a transmitter chain of the electronic equipment, saidphase-shifts occurring as time discrete phase jumps in response tochanging the output power.

This object is achieved by an electronic equipment comprising the deviceaccording to the invention. In one embodiment, the equipment is a mobileterminal, a pager or a communicator. In another embodiment, theelectronic equipment is a mobile telephone.

An advantage of the present invention is that it is possible toimplement the device in the digital domain, wherein the electronicequipment will consume almost no extra power. Also, if the storage meansis a rewritable memory, the stored phase change values may be altered inthe future to meet technology changes in the communication system.

Further preferred features of the invention are defined in the dependentclaims.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the present invention will be described in relation tosome embodiments and accompanying drawings, in which:

FIG. 1 illustrates a mobile terminal comprising the device according tothe invention, and a base station;

FIG. 2 is a block diagram of a wave form generator connected to thedevice according to the invention;

FIG. 3 a illustrates a first embodiment of a look-up table according tothe invention;

FIG. 3 b illustrates a second embodiment of a look-up table according tothe invention;

FIG. 3 c illustrates a third embodiment of a look-up table according tothe invention;

FIG. 4 is a flow chart of a method for deriving phase change valuesstored in any of the look-up tables illustrated in FIG. 3 a-3 c; and

FIG. 5 is a flow-chart of a method according to the invention for addinga phase offset signal to the input signal at an amplifier means.

DETAILED DESCRIPTION OF EMBODIMENTS

Various mobile communication systems utilize fixed base stations forcommunicating with mobile terminals via a wireless interface. Suchsystems include code division multiple access (CDMA) systems, such asthe wide band multiple access (WCDMA) system employed in the universalmobile telecommunication system (UMTS).

FIG. 1 illustrates an electronic equipment embodied as a mobile terminal1, which according to the invention comprises a device 46 forpredistorting an input signal at an amplifier of a transmitter chain ofthe mobile terminal 1. The device of the invention is adapted to add aphase offset to the input signal in response to a change of the outputpower of the mobile terminal. As is understood, the electronic equipmentmay take other forms, such as a mobile telephone, a pager, or acommunicator, without departing from the scope of the invention.However, for convenience reference will be made to a mobile terminal 1throughout this description. Further, the mobile communication systemcomprises at least one base station 2, with which the mobile terminal 1may communicate speech and data according to a predetermined protocolover a wireless link 3. The mobile terminal 1 comprises a man machineinterface, with which a user of the mobile terminal 1 may operate saidterminal. The man-machine interface may comprise, but is not limited to,a display 10, a keypad 11, a microphone 12, and a loudspeaker 13.Further, the mobile terminal comprises an antenna 14 for transmittingsignals to the base station 2. The antenna 14 is connected to thetransmitter chain within the mobile terminal 1.

FIG. 2 illustrates a waveform generator 20 being part of the transmitterchain of the mobile terminal 1 comprising the device according to thepresent invention. The waveform generator 20 comprises first and secondtransmitter filters 21, 22 for filtering the in-phase (I) component andthe quadrature (Q) component of a base band signal, respectively.Further, a first mixer 23 is provided prior to the filters 21, 22 formixing the base band signal with the scrambling code of the mobileterminal 1. The waveform generator 20 is adapted to generate a base bandsignal to be supplied as the input signal to an amplifier means 30 via aRF (radio frequency) modulator 31.

To provide changing of the output power of the output signal of thetransmitter chain the amplifier means 30 is in one embodiment a variablegain amplifier (VGA). The gain of the variable gain amplifier may e.g.be set according to predetermined levels in order to set the outputpower level of the transmitter to meet requirements of differentspecifications. Power levels and classes are e.g. specified in the thirdgeneration partnership project (3GPP) specification TS 25.101, which isincorporated herein by reference. However, the exact number of powerclasses or power levels of the output power is not important for thepresent invention, wherein any number of classes or levels may beimplemented.

A power controller 40 sets the gain levels of the amplifier means 30 tokeep the output power at a desired level. Consequently, the powercontroller 40 is connected to the amplifier means 30 to control theoutput power of the amplifier means in any number of predeterminedlevels. The exercise of the control of the gain levels of the amplifiermeans 30 to adjust the output power may be executed in a number ofdifferent ways. In open loop power control, the mobile terminal 1determines an estimate of the path loss between the base station 2 andthe mobile terminal 1 by measuring the received signal strength at themobile terminal 1. An automatic gain control (AGC) circuitry (not shown)within a receiver chain 45 of the mobile terminal 1 provides a roughestimate of the propagation loss for each mobile terminal 1. The smallerthe received power the larger the propagation loss, and vice versa. Thetransmit power, i.e. the output power, of the mobile terminal 1 is inone embodiment determined from the equation:mean output power (dBm)=−mean input power (dBm)+offset power+parameters.The offset power is e.g. −73 dB for the 800 MHz band mobile terminal and−76 dB for the 1900 MHz mobile terminals in the IS-95 standard (US CDMAsystem).

The desired output power level is then supplied by the receiver chain 45to the power controller 40. The parameters are used to adjust the openloop power control for different cell sizes and different cell effectiveradiated powers (ERP) and receiver sensitivities. The parameters areinitially transmitted on the synchronization channel between the mobileterminal 1 and the base station.

In another embodiment closed loop power control is utilized, wherein atransmit power control (TPC) command is received in the downlink by thereceiver chain 45 of the mobile terminal 1. Said command is derived bythe base station 1 based on the received signal strength of the signalfrom a specific mobile terminal 1. The power controller 40 is connectedto the receiver chain 45 in order to receive the TPC commands and setthe gain level of the amplifier means 30 accordingly. The receiver chain45 does not form any part of the present invention, and is therefore notfurther disclosed herein. In one embodiment of the invention, the powercontroller 40 forms part of the amplifier means 30.

As discussed above, the change of the gain level of the amplifier means30, and consequently the output power, will add a phase-shift to theoutput power of the output signal from the amplifier means 30. Thephase-shift will occur as a time discrete phase-jump of the output powerin response to the change of the output power. To compensate for suchphase-shifts, a phase offset signal is added to the base band signal,which is generated by the waveform generator, by means of the device 46according to the invention for predistorting the input signal at theamplifier means 30. In one embodiment, the phase offset signal is acomplex value having amplitude corresponding to 1 and a phase valuecorresponding to a phase offset value, which will be described below.Therefore, the device 46 comprises a phase offset adding means 50, suchas a digital multiplier or a complex multiplier, that mixes the baseband signal from the waveform generator 20 with the phase offset signal.In the embodiment illustrated in FIG. 2, the phase offset adding means50 is provided after the waveform generator, i.e. after the first andsecond transmitter filters 21, 22. However, in alternative embodiment,the phase offset adding means 50 is a part of the waveform generator 20,wherein the phase offset adding means 50 is provided before the transmitfilters 21, 22. As is understood, also other positions of the phaseoffset adding means 50 is possible within the scope of the invention, aslong as the phase offset may be added to the input signal at theamplifier means 30.

The device 46 according to the invention further comprises a storagemeans 51 and an offset controller 52. The storage means 51 is in oneembodiment a memory, wherein at least one value of the change of thephase of the output power for different gain levels of the amplifiermeans 30 is stored in a look-up table 53 a, as will be further explainedin the following. In one embodiment, the storage means 51 is arewritable memory, wherein the phase change values stored in said memorymay be substituted. In another embodiment, the storage means 51 is aread only memory (ROM), wherein the values of the look-up table 53 a arestored by the manufacturer of the mobile terminal 1 according to apredetermined specification.

FIG. 3 a illustrates a first embodiment of the look-up table 53 a storedin the storage means 51. The look-up table 53 a comprises columns,wherein different gain levels G_(i) (G_(i)=G₁ . . . G_(n)) of theamplifier means 30 is stored in a first column, and phase change valuesC_(i) (C_(i)=C₁ . . . C_(n)) associated with each gain level are storedin a second column. Consequently, phase change value C₁ corresponds to achange of the phase of the output power when the gain is changed fromgain level G₀ to gain level G₁ etc. A phase change value will not bestored for the lowest gain level G₀. In one embodiment, each phasechange value is a digital phase value, which may be retrieved by theoffset controller 52. Consequently, the storage means 51 is connected tothe offset controller 52 being connected to the power controller 40. Inan alternative embodiment, the power controller 40 and the offsetcontroller 52 are provided as one controller providing the functions ofthe separate controllers 40, 52.

When it is decided that the gain level of the amplifier means 30 shouldbe changed, i.e. increased or decreased as indicated by the open orclosed loop power control as described above, the power controller 40transmits a gain control signal to the amplifier means 30 instructingsaid amplifier means 30 to change its gain level. Also, the powercontroller 40 transmits a gain change indication signal to the offsetcontroller 52 indicating that the gain of the amplifier means 30 is tobe changed. The gain change indication signal comprises information ofthe new gain level of the amplifier means 30. In response thereto, theoffset controller 52 retrieves from the storage means 51 the phasechange values corresponding to the new gain level by addressing thestorage means by means of the new gain level. Then, the phase offsetvalue is outputted, as will be explained below.

In an alternative embodiment the output power, and consequently the gainlevel, of the amplifier means 30 is compensated for temperaturedependent phase-shifts in connection with the gain level dependentphase-shift. Therefore, a temperature sensing means 60, such as atemperature sensor, is connected to the offset controller 52.

FIG. 3 b illustrates one embodiment of a second look-up table 53 bcomprising phase change values being dependent on the gain level of theamplifier means 30 as well as the temperature. The temperature may bedivided into different temperature intervals T_(i), such as 0-5° C.,5-10° C. etc., to limit the needed storage space. The specific number oftemperature intervals (T₁ . . . T_(n)) has to be tested and evaluated ineach specific case. As in the embodiment illustrated in FIG. 3 a, thelook-up table 53 b comprises columns, wherein different gain levels ofthe amplifier means 30 is stored in a first column, and the associatedphase change value is stored in a second column. However, here thelook-up table 53 b comprises a third dimension, wherein the gain levelsG_(i) and the associated phase change values C_(i) are stored for eachtemperature interval T_(i). In this embodiment, the offset controller 52has to provide both information of the second, i.e. the new, gain levelof the amplifier means 30 as well as temperature information to thelook-up table 53 b to retrieve the correct phase change value, whereinthe temperature value or the temperature interval value is an index toaddress the look-up table 53 b together with the new gain level.

In another embodiment, the device 46 according to the inventioncompensates for frequency dependent phase-shifts or frequency banddependent phase-shifts of the output signal of the amplifier means 30.In this embodiment, the device 46 according to the invention comprises afrequency indicator 70 connected to the offset controller 52, which maydivide each specific frequency into different frequency intervals F_(i)(F_(i)=F₁ . . . F_(n)). The frequency indicator indicates the operatingfrequency and/or the operating frequency band of the mobile terminal 1.FIG. 3 c, illustrates a look-up table 53 c comprising data having phaseshift change values C_(i) depending on both gain level G_(i) of theamplifier means 30 as well as the frequency intervals F_(i). In thisembodiment, the offset controller 52 has to provide both information ofthe first and second gain levels of the amplifier means 30 as well asfrequency interval information to the look-up table 53 b to retrieve thecorrect phase change values, wherein the frequency value or thefrequency interval value is an index to address the look-up table 53 ctogether with the new gain level of the amplifier means 30.

In still another embodiment the device 46 according to the inventioncompensates both for frequency dependent and temperature dependentphase-shifts in addition to gain level dependent phase-shifts. In thisembodiment, a number of look-up tables are provided, wherein each tablecorresponds to either the embodiment shown in FIG. 3 b or 3 c, and beingvalid in a specific temperature interval or a specific frequencyinterval. The specific look-up table may be addressed, by means of thetemperature interval or the frequency interval information, to accessingthe specific phase change values corresponding to certain first andsecond gain levels and a certain temperature interval or frequencyinterval.

The phase change values to be stored in the storage means 51 may bedefined according to the steps illustrated in the flow chart of FIG. 4and described in the following:

First, in step 100 supply an input signal generated by a waveformgenerator 20 without any phase offset adding means 50 according to theinvention, or with the phase of phase offset set to 0, to the amplifiermeans 30 being set to the lowest gain level G₀. Keep the temperatureconstant at a predetermined level, such as room temperature.

In step 101, measure and temporarily store the phase of the output powerfrom the amplifier means 30 to provide a phase reference value.

In step 102, increase the output power with a predefined value, such as1 dB, by increasing the gain level of the amplifier means 30.

Then, in step 103 measure the phase of the output power from theamplifier means 30.

In step 104, calculate the value of the change in phase, between thechanged phase measured in step 103 and the phase reference valuecalculated in step 101, and store said change value in the look-up table53 a of the storage means 51 at the gain level set in step 102 as acorresponding phase change value C_(i). Consequently, increasing thegain level from the first, or lowest, gain level G₀ to the second gainlevel G₁ will generate a first phase change value C₁ corresponding tothe second gain level G₁.

In step 105, decide whether the gain level of the amplifier means 30 hasreached its highest gain level G_(n). If not, the procedure is returnedto step 102 to derive a subsequent phase change value C_(i+1). However,if the decision in step 105 if affirmative, in step 106 the procedure isended.

The method illustrated in steps 100-106 of FIG. 4 may be repeated fordifferent temperatures or temperature intervals, wherein the temperaturechosen is preferably in the middle of the temperature interval iftemperature dependent phase offset signals should be provided. This willgenerate a look-up table 53 b according to FIG. 3 b. As is understood,the method in step 100-106 may also be repeated for different operatingfrequencies or operating frequency intervals of the mobile terminal 1,wherein the operating frequency is kept constant throughout one cycle,100-106. The chosen operating frequency in each frequency interval ispreferably chosen in the middle of the frequency interval. The procedureis then repeated for any required operating frequency or frequencyinterval. Also, the procedure in FIG. 4 may equally be repeated fordifferent temperature intervals and frequency intervals to generatechange phase change values being both frequency and temperaturedependent.

In CDMA technology information data is sent to the base station 2 inslots having a small time gap between subsequent slots. During the timegap no information data is transmitted to the Base station. The controlof the gain level of the amplifier means 30 is preferably executedduring the time gap as the changing of the gain level will generate asmall transient in the output signal although the phase offset signal isadded to the input signal. However, if the changing of the gain level ofthe amplifier means 30 and the adding of the phase offset signal to theinput signal at the amplifier means 30 is synchronized during the timegap the transient will not be detrimental, as no information data istransmitted.

FIG. 5 illustrates the method for predistorting the input signalaccording to the invention for compensating for phase changes due to again level change of the amplifier means 30. In the preferredembodiment, the steps according to the method are executed in the timegap wherein no transmission of information data is provided. The neededphase compensation of the input signal at the amplifier means 30 iscalculated by the offset controller 52 and supplied as the phase offsetsignal to the phase offset adding means 50. In a first step 200, anindication to change the output power to a certain level, such as theTPC command, is received by the power controller 40. In step 201, thenew gain level of the amplifier means 30 is determined based on theindication received in step 200. In step 202, in response to determiningthe new gain level, or changing the gain level, the new gain level ofthe amplifier means 30 is indicated by the power controller 40, i.e.supplied to the offset controller 52, which will be an index foraddressing the lookup-table 53 a of the storage means comprising gainlevels and associated phase values. Each gain level stored in thelook-up table have an associated phase value. Therefore, the offsetcontroller 52 will retrieve a phase value corresponding to the new gainlevel of the amplifier means 30.

In step 203, if the offset signal should compensate for temperatureand/or frequency dependent phase-shifts, the offset controller 52obtains the temperature supplied by the temperature sensing means 60,and/or the frequency or the frequency band supplied by the frequencyindicator 70. Then, the temperature interval and/or the frequencyinterval may be derived. If the temperature and/or frequency are notneeded, step 203 is omitted. Then, in step 204 the new gain level of theamplifier means 30 together with the frequency/frequency interval and/orthe temperature/temperature interval are used to address the storagemeans 51 to retrieve an associated temperature/frequency dependent phasevalue, i.e. a change value C_(i), which corresponds to the new gainlevel. The new gain level, possibly together with the temperature (ortemperature interval) and the frequency (or frequency interval or band),acting as an index to address the look-up table 53 a, 53 b, 53 c aresupplied to the storage means 51, which returns the demanded phasechange value. However, if the new gain level of the amplifier means 30is the basic gain level, no change value needs to be retrieved, as thechange value relating to the basic gain level is known to be zero.However, as is understood, a change value may also be stored for thebasic gain level. Finally, in step 205 the power controller 40 suppliesthe new gain level to the amplifier means 30, which will provide theoutput power level indicated by the change indicator. Also, the offsetcontroller 52 supplies the value of the phase offset signal to the phaseoffset adding means 50, which will add said offset to the input signalgenerated by the waveform generator. If the gain level is changed andthe value of the phase offset signal is added to the input signal at theamplifier means 30 during the time gap, no detrimental phase jump willbe added to the output signal from the mobile terminal 1.

The present invention has been described in some embodiments. However,the scope of the invention should not be limited to the above-describedembodiments, but is best defined by the following independent claims.Furthermore, the term “comprising” does not exclude other elements orsteps, the terms “a” and “an” do not exclude a plurality and a singleprocessor or other unit may fulfill the functions of several of theunits recited in the claims. The function of the offset controller 52may e.g. be implemented as software comprising computer readableinstructions for carrying out the functions of said controller whenexecuted by a processing unit, such as the central processing unit ofthe mobile terminal 1.

1. A device for predistorting an input signal at an amplifier means,comprising a storage means, an offset adding means, and a controller,wherein the storage means is adapted to store phase values; the offsetadding means is a phase offset adding means for phase-shifting the inputsignal, the storage means and the phase offset adding means areconnected to the controller, which is adapted to retrieve at least onephase value from the storage means, and output an offset signalcomprising the retrieved phase value to the phase offset adding means,which is adapted to add said offset signal to the input signal, and thestorage means comprise a lookup table comprising different gain levelsand associated phase values, and the controller is adapted to retrieve aphase value from the storage means corresponding to a given gain levelof the amplifiers means.
 2. A device for predistorting an input signalat an amplifier means, comprising a storage means, an offset addingmeans, and a controller, wherein the storage means is adapted to storephase values; the offset adding means is a phase offset adding means forphase-shifting the input signal, the storage means and the phase offsetadding means are connected to the controller, which is adapted toretrieve at least one phase value from the storage means, and output anoffset signal comprising the retrieved phase value to the phase offsetadding means, which is adapted to add said offset signal to the signal,and the storage means is a memory comprising a look-up table comprisingphase values relating to the change of the gain level of an amplifiermeans from a first gain level to one or more additional gain levels. 3.The device according to claim 2, wherein the memory is rewritable. 4.The device according to claim 1, wherein the phase offset adding meansis a complex multiplier.
 5. A device for predistorting an input signalat an amplifier means, comprising a storage means, an offset addingmeans, and a controller, wherein the storage means is adapted to storephase values; the offset adding means is a phase offset adding means forphase-shifting the input signal, the storage means and the phase offsetadding means are connected to the controller, which is adapted toretrieve at least one phase value from the storage means, and output anoffset signal comprising the retrieved phase value to the phase offsetadding means, which is adapted to add said offset signal to the inputsignal, and each phase value stored in the storage means corresponds toa change in phase of the output power when the gain level of theamplifier means is changed from a first gain level to a second gainlevel.
 6. The device according to claim 5, wherein the first gain levelis the lowest gain level, and the second gain level is any other gainlevel of the amplifier means.
 7. A device for predistorting an inputsignal at an amplifier means, comprising a storage means, an offsetadding means, and a controller, wherein the storage means is adapted tostore phase values; the offset adding means is a phase offset addingmeans for phase-shifting the input signal, the storage means and thephase offset adding means are connected to the controller, which isadapted to retrieve at least one phase value from the storage means, andoutput an offset signal comprising the retrieved phase value to thephase offset adding means, which is adapted to add said offset signal tothe input signal, and the device further comprises a temperature sensingmeans connected to the controller for deriving a temperature or atemperature interval, and the storage means comprises a lookup tablecomprising gain levels and associated phase values for differenttemperatures or different temperature intervals, and the controller isadapted to retrieve a temperature dependent phase value from the storagemeans corresponding to a temperature or temperature interval and a givengain level of the amplifier means.
 8. A device for predistorting aninput signal at an amplifier means, comprising a storage means, anoffset adding means, and a controller, wherein the storage means isadapted to store phase values; the offset adding means is a phase offsetadding means for phase-shifting the input signal, the storage means andthe phase offset adding means are connected to the controller, which isadapted to retrieve at least one phase value from the storage means, andoutput an offset signal comprising the retrieved phase value to thephase offset adding means, which is adapted to add said offset signal tothe input signal, and the device further comprises a frequency indicatorfor deriving an operating frequency value or an operating frequencyinterval value, and the storage means comprises a lookup tablecomprising gain levels and associated phase values for differentfrequencies or different frequency intervals, and the controller isadapted to retrieve a frequency dependent phase value from the storagemeans corresponding to a frequency or frequency interval and a givengain level of the amplifier means.
 9. A method for predistorting aninput signal at an amplifier means including a storage means, comprisingthe steps of: retrieving a phase value from a lookup table of thestorage means in response to changing a gain level of the amplifiermeans; and adding an offset signal having a phase value corresponding tothe retrieved phase value to said input signal; wherein the step ofretrieving further comprises the steps of: receiving a new gain level ofthe amplifier means; and retrieving a phase value associated with thenew gain level from the look-up table of the storage means.
 10. A methodfor predistorting an input signal at an amplifier means including astorage means, comprising the steps of: retrieving a phase value from alookup table of the storage means in response to changing a gain levelof the amplifier means; and adding an offset signal having a phase valuecorresponding to the retrieved phase value to said input signal; whereinthe phase value corresponding to a basic gain level is zero.
 11. Themethod according to claim 9, wherein the step of retrieving furthercomprises the steps of: obtaining a temperature value or a temperatureinterval value; and retrieving a temperature dependent phase valueassociated with the new gain level and the temperature or temperatureinterval from the lookup-table of the storage means.
 12. The methodaccording to claim 9, wherein the method comprises the further steps of:obtaining a frequency value or a frequency interval value; andretrieving a frequency dependent phase value associated with the newgain level and the frequency or frequency interval from the look-uptable of the storage means.
 13. The device according to claim 1, whereinthe device is a mobile terminal, a pager, or a communicator.
 14. Thedevice according to claim 1, wherein the device is a mobile telephone.15. The device according to claim 2, wherein the phase offset addingmeans is a complex multiplier.
 16. The device according to claim 5,wherein the phase offset adding means is a complex multiplier.
 17. Thedevice according to claim 7, wherein the phase offset adding means is acomplex multiplier.
 18. The device according to claim 8, wherein thephase offset adding means is a complex multiplier.